Microtubules represent one of the three essential cytoskeleton types in cells. Important for a variety of physiological functions, encompassing cell migration, mitosis, neuronal differentiation and transport of cargo, microtubule-associated motor proteins have been implicated in numerous diseases, ranging from motor neuron and degenerative disorders, to neoplasia and viral infections. Microtubule-binding CAP-Gly domains are conserved in organisms from human to yeast, play central roles in many proteins, and their mutations lead to various disorders. CAP-Gly domain of the p150glued subunit of dynactin interacts with microtubules, and its mutations are associated with several motor neuron disorders. The atomic-level structure and dynamics of CAP-Gly/microtubule assemblies are not known because of their inherent insolubility and lack of long-range order. Lack of such insight hampers further research and impedes design of effective therapies against diseases associated with cytoskeleton dysfunction. Our long-term goal is to understand the structural and dynamic basis of cargo transport regulation along microtubules by microtubule-associated proteins, in healthy and disease states. The objectives of this application are to determine three-dimensional structures and dynamics of CAP-Gly domain of dynactin and of its macromolecular assemblies with the microtubules and with EB1 protein. We will employ multidimensional high-resolution magic angle spinning solid-state NMR methods in conjunction with biophysical and biochemical techniques. In the specific aims designed to accomplish the objectives of this application, we will: 1) determine the structure of CAP-Gly alone and CAP-Gly assembled on the microtubule, and identify the CAP-Gly/microtubule interface at atomic resolution; 2) characterize the energetics and dynamics of the CAP-Gly/microtubule interaction; 3) characterize the dynamics of CAP-Gly mutants related to neurological pathologies; 4) characterize biochemically and structurally the regulation of the CAP- Gly/EB1/microtubule interaction. The proposed work has important implications for human health as it will shed light on the structure of CAP-Gly:microtubule complexes that are not amenable to structural characterization by X-ray crystallography or solution NMR spectroscopy, and will enable structural characterization of macromolecular assemblies consisting of microtubule-associated proteins in complexes with microtubules.